GPU-native MLP networks that use CudaLinear layers + cuBLAS sgemm
internally. These are drop-in replacements for the Candle-based
PolicyNetwork and ValueNetwork, providing the same forward/softmax/
log_softmax API surface but with zero Candle overhead.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>